New therapies are crucial for prostate cancer. The overall aim of this project is to continue to test, develop, refine, and translate to clinical trials, ex vivo and in vivo, human gene therapy for androgen refractory prostate cancer (PCA). The hypothesis stimulating this research is that hormone refractory prostate cancer can be treated effectively using human gene therapy strategies. In the first three years of the S.P.O.R.E., we have identified one rational strategy of ex vivo gene therapy which can eradicate preclinical models of metastatic PCA. With unanticipated speed, this S.P.O.R.E. project generated sufficient clinical feasibility data for translation to N.I.H. Recombinant Advisory Committee and Johns Hopkins I.R.B. approval of the first ever human gene therapy clinical trial for prostate cancer. The proposed research in the 5-year continuation of this project contains additional preclinical mechanistic and pharmacodynamic studies with a view toward informing the Phase II (efficacy) testing of GM-CSF gene therapy for prostate cancer. In parallel, a second research direction of in vivo gene cytoreductive gene therapy of prostate cancer will be tested for its potential translation to S.P.O.R.E. clinical trials. The pharmacodynamics of a replication-defective, highly efficient retrovirus (MFG) and a novel replication-defective adenovirus (Ad5mfg) will be compared for optimal therapeutic vector performance. For in vivo gene therapy, identification of toxins which are especially cytotoxic to human prostate cancer cells is required. These toxins can be used as "suicide" genes for a bystander effect in gene therapy strategies which employ prostate organ-specific promoters such as the PSA promoter. Ideally, these strategies should inflict non-cell-cycle specific killing of prostate cancer cells refractory to androgens and chemotherapy. A high throughput screen of cytotoxic cDNA constructs will be tested against human prostate cancer cell lines to identify the most potent cytotoxic molecules as lead compounds for in vivo gene therapy. Testing the utility of using replication-defective adenoviral (Ad5) vectors may allow for delivery of identified cytotoxic cDNAs for preclinical efficacy testing in human prostate cancer xenografts. Translation to Phase I/II studies of in vivo cytoreductive gene therapy for human prostate cancer in the years 1997-1998 is an overall objective of this portion of the project.